The present invention relates to both a method of fabricating a single-crystalline silicon film with the use of a laser or electron beam and an apparatus for performing the method.
A single-crystalline silicon film to be used in a semiconductor device is usually fabricated by a CVD (i.e., Chemical Vapor Deposition) method or an evaporation method. There has recently been proposed a method, in which a silicon film of a non-single-crystalline type is irradiated with a laser or electron beam so that the film is annealed to form a single-crystalline silicon film. On pages 116 to 152 of NIKKEI ELECTRONICS published in Japan on June 6, 1979, for example, there is found a description that an amorphous thin silicon layer is formed on the surface of a single-crystalline substrate and is irradiated with a laser so that the amorphous layer can be epitaxially formed as a single crystalline layer on the substrate. On pages 64 to 71 of Electronic Materials published in Japan in November, 1978, moreover, there is also found a description that, if a semiconductor surface layer of silicon is placed for a short time period in a melted condition by an electron beam in an annealing treatment, the melted region is epitaxially recrystallized from the interface of the substrate and the melted region to form a single-crystalline layer.
The annealing methods using the laser and electron beams are different in that the laser utilizes optical energy; whereas the electron beam utilizes electrical energy, but the methods are identical in that the non-single-crystalline surface layer is annealed in a liquid phase while maintaining a sample (i.e., a semiconductor material) as a whole at a low temperature. According to these annealing methods, the various disadvantages, which have caused problems in the conventional annealing method in an electric furnace, due to the annealing treatment at a high temperature, for example, the crystal defect, the contamination and the impurity diffusion from the higher doped substrate can be reduced effectively.
In an annealing method using a laser or an electron beam (which beam will be referred to as "the laser or the like"), however, there is a limit in the thickness of the surface layer, which makes the annealing treatment possible, in accordance with the output energy level of the laser or the like. The inventors have effected single-crystallization of a polycrystalline silicon film, formed on a single-crystalline substrate by an experimentally prepared laser device, and have confirmed that it is difficult to form excellent single-crystals on the polycrystalline silicon film over all of the film thickness, if the thickness of the polycrystalline silicon film exceeds 5000 A. Therefore, in order that a single-crystalline silicon film having such a thickness, as is required for fabricating a semiconductor device, may be formed by an annealing method using the laser or the like, both the step of forming a substrate with a polycrystalline silicon film having a thickness smaller than the annealable thickness and the step of irradiating and annealing the polycrystalline silicon film formed with the laser or the like so that the polycrystals may be single-crystallized are to be repeated several times. Each time the growth of the polycrystals and the irradiation with the laser or the like are effected, however, the substrate has to be brought into and out of the CVD device (or evaporation device) and the laser irradiating device so that the procedures therefor are remarkably complicated. Even if the insertion and take-out at the respective devices are not required, on the other hand, the work management of the conditions at the respective CVD or evaporation and laser irradiation steps becomes remarkably complex and tedious.
As a result, a method of fabricating a single-crystalline silicon film by an annealing treatment using the laser or the like has not been completed, although theoretically and experimentally possible, to such an extent that the fabrication of such a thick single-crystalline silicon film, as is required by a semiconductor device, is put into practice and that the aforementioned various advantages resulting from the laser annealing method can be substantially attained.